The HTTP specification dictates that any response must have a three-digit status code that allows programs to determine the nature of the response. These codes allow a program to process the response efficiently:
| Status code | Class of response | Description |
| 1xx | Informational | The request was received but not yet fully processed. The client doesn't need to do anything. |
| 2xx | Success | The request was successfully received, understood, and accepted. |
| 3xx | Redirection | The resource has moved, either temporarily or permanently. The client needs to take further actions to complete the request. |
| 4xx | Client error | The request is syntactically and/or semantically incorrect, and the server was unable (or refused) ... |
